Toshitaka Hidaka

Genetic diversity and structure of urban populations of Pieris butterflies assessed using amplified fragment length polymorphism.

Conservation programs in urban ecosystems need to determine the genetic background in populations of urban dwellers. We examined the genetic diversity and structure of Pieris rapae and P. melete using AFLP markers, and compared them between species and between urban and rural environments. As a result: (i) in both species, there was no reduction in genetic diversity within urban populations by direct comparison of diversity measurements, although the analysis of molecular variance suggested significant reductions in the variance within seasonal subpopulations in urban populations; (ii) P. rapae retained greater genetic diversity within species and populations; (iii) populations of both species showed significant genetic differentiation, and P. melete was more strongly subdivided; (iv) in both species, geographically close populations did not cluster with one another in the upgma analysis; (v) there was no genetic isolation due to geographical distance in either species; (vi) the genetic composition of seasonal subpopulations differed in urban populations of both species, and the genetic distances among subpopulations were correlated with seasonal differences in P. rapae and with temporal differences in P. melete. These results indicate that the genetic diversity in urban populations of both species was reduced at times, but was maintained by dispersal from genetically differentiated populations. Differences in the ability and mode of dispersal in the two species may be reflected in the degree of population subdivision and patterns of seasonal change in the genetic composition.

Comparison of the mating behaviour between two sympatric species,Nezara antennata andN. viridula (Heteroptera: Pentatomidae), with special reference to sound emission

Mating behaviour and associated songs were compared between 2 sympatric congeneric species,Nezara antennata andN. viridula, between which interspecific mating was known to occur under natural conditions. The fundamental sequence of mating behaviour for these species was the same. Three kinds of songs were recorded from each sex ofN. antennata. ForN. viridula, 4 kinds of male songs and 3 kinds of female songs were recorded. The songs which corresponded with definite behavioural bouts were distinct between these species. Some consideration was made as to why interspecific differences in the songs did not sufficiently engender ethological isolation. In addition, some geographic variations in the songs were shown among Yugoslavian (Čokl et al. 1972), American (Harris et al. 1982) and Japanese populations ofN. viridula. These variations were relatively inconspicuous when compared with the interspecific differences fromN. antennata.

Semilunar Rhythm in the Zoea-Release Activity of the Land Crabs Sesarma*

SummaryThe number of the land crabs Sesarma which released zoeae in a river was counted and recorded for 2 years. The number of crabs releasing zoeae reached a maximum at around every syzygy and decreased to a minimum at around every half moon, showing a semilunar rhythm (Fig. 2). This semilunar rhythm, when examined temporally, showed a peculiar pattern accurately synchronized with the lunar cycle. On the day of and during 4–5 days prior to the syzygy, the peak of zoea-release activity came just after sunset. A few days later, the peak gradually shifted to later in the evening and became flattened until temporal concentration was no longer observed. About 2 days after the half moon, the peak appeared again just after sunset (Figs. 3, 4 and 5). It is not likely that the tide itself affects the semilunar rhythm of Sesarma, but it is supposed that the lunadian factor is involved in it. The adaptive significance of this semilunar rhythm may be interpreted to mean that zoeae released in the river just after the time of spring high tides will successfully arrive at the sea and that the lunadian modification of the peak in the temporal structure will also ensure that the zoeae will be released at the time of high tides and will have a better chance of arriving at the sea than they would otherwise do.

Effects of the gregarious parasitoids, Apanteles ruficrus and A. Kariyai, on host growth and development

Abstract Two gregarious parasitoids, Apanteles ruficrus and A. kariyai attack larvae of the common armyworm, Pseudaletia separata . Their growth pattern and growth rate of the parasitoids were not affected by host age at the time of oviposition, even though host weight increased exponentially with age. Consequently, the maximal weight of a single parasitoid larva was nearly constant regardless of host instar parasitized. Parasitoid females laid more eggs in later-instar hosts than in earlier-instar hosts. When parasitized at the same age, heavily parasitized hosts attained a larger mass than lightly parasitized larvae. Therefore, the ratio of the maximal weight of the host to the parasitoid mass was nearly constant. These results indicate that host growth is regulated by the parasitoids.

Reproductive strategy and interspecific competition in the Lake-living gobiid fish isaza,Chaenogobius isaza

Isaza,Chaenogobius isaza, is a small gobiid fish endemic to Lake Biwa. It lives offshore throughout almost the entire year, showing a remarkable diel vertical migration. In early spring, males and females migrate to lake shore to spawn under stones. Spawning season is limited to a very short span of time in early spring, late April to early May. During this short spawning season, the male is supposed to have only 2 brood cycles at maximum. At each brood cycle, the male is strictly monogynous, never accepting additional females. Males therefore show a marked mate choice, choosing a larger female regardless of the size of the male himself. Females also choose larger males. However, males are supposed to not waste time in male-male fighting in the natural spawning area. That this very short spawning season and its occurrence in early spring is primarily to avoid interspecific competition with another littorally reproducing goby Yoshinobori,Rhinogobius brunneus, is experimentally demonstrated.

Mating system ofTokunagayusurika akamusi (Diptera: Chironomidae): I. Copulation in the air by swarming and on the ground by searching

Observations on the mating system of the midge,Tokunagayusurika akamusi, revealed mating to occur both in the air by swarming and on the ground by searching. At the shores of Lake Biwa, midges appeared from November to early December. Newly emerged adults arrived at the resting place, lakeside vegetation, in the morning, during which time a number of males also walked about in search of mates. Many copulating pairs were observed at the resting place. Huge swarms occurred chiefly before sunset but the frequency of copulation observed in the swarm was extremely low. It is likely that, in the Lake Biwa population, the proportion of females inseminated by searching males at the resting place was much larger than that by swarming males in the air. Furthermore, by searching, males copulated with younger females than by swarming. The differences between the searching and swarming tactics are discussed.

Neuroendocrine mechanism involved in pupal colour dimorphism in swallowtail Papilio xuthus L.

Neuroendocrine mechanism involved in pupa) colour dimorphism in Papilio xuthus L. has been studied using ultrastructural techniques. The browning hormone in the form of neurosecretory material is secreted in the brain during the larval stage and transported to the axonal endings in the prothoracic ganglion, irrespective of the colour of the future pupa. If larvae select for pupation environmental conditions that are conducive for the formation of a brown pupa, release of the browning hormone occurs in the middle of the prepupal stage. No release occurs in larvae that have selected environmental conditions that favour the formation of green pupae. It is suggested that the brain, having integrated and interpreted the environmental conditions selected by the larva for pupation, gives the order to release the browning hormone. Such an order is conveyed via neural path from the brain to either the prothoracic ganglion, or some still unknown neurohaemal organ associated with it, from which release then takes place.

Role of the brain in post-diapause adult development in the swallowtail, Papilio xuthus

Abstract The role of the brain in adult development was examined by brain removal in unchilled and chilled diapausing pupae of Papilio xuthus . Chilling was effective in shortening the pupal duration and synchronizing adult emergence, although photoperiod had little effect on diapause development. The brain played a role of shortening the pupal duration and synchronizing adult emergence in both unchilled and chilled individuals, although it was not essential for post-diapause adult development. The stimulus of low temperature was recorded even in the absence of the brain, because chilling shortened the pupal duration in brainless individuals. The brain showed activity which affected subsequent adult development in chilled pupae within one day after chilling in males. This period was less limited in females.

The mating system ofTokunagayusurika akamusi (Diptera; Chironomidae): II. Experimental analysis of male mating behaviour at the resting place

Mating behaviour ofTokunagayusurika akamusi searching at the resting place (lakeside vegetation, although mating also occurs in the air by swarming) was investigated at the shore of Lake Biwa. Coinciding with the arrival of newly emerged adults, previously emerged males walked about to search for mates at the resting place. When a searching male came into contact with a fresh (newly emerged) individual, he attempted to copulate with it regardless of its sex. Consequently, males copulated with fresh females, which were more likely to be virgin at the resting place, suggesting that the first male might contribute best to the fertilization.

Feeding behaviour of the Japanese loach,Misgurnus anguillicaudatus (Cobitididae)

The feeding behaviour of a Japanese loach,Misgurnus anguillicaudatus was experimentally analyzed. From observations the behaviour patterns were described. The adult fish responded to a piece of thread soaked with filteredTubifex homogenate (Tubifex solution) and showed feeding behaviour. But they ignored an unsoaked piece of thread. LivingTubifex kept in a glass cell failed to elicit feeding behaviour in the fish. A gauze-covered vessel withTubifex solution buried in the sand substrate released feeding behaviour in fish in its vicinity. It follows that the feeding behaviour of this fish is induced by some chemical stimuli. WhenTubifex solution was introduced at the central area of the plastic vessel with a fish, the fish suddenly started the Feeding-crawl and showed Gulp which was composed of Dig and Twist. Using sand particles, it was shown that intake of materials into the digestive tract occurs only at the moment of Twist and not any other time. The standard feeding patterns ofMisgurnus anguillicaudatus are thus quick inhalation of organic matter together with substrate, occurring at the moment of Twist, which is released at the place where the fish received the appropriate chemical stimuli.Misgurnus anguillicaudatus is regarded as a typical “detritus feeder”.